In performing the calculations required to display a computer generated hologram (CGH) using an interference based algorithm, it is necessary to populate the object to be displayed with an array of points that, when seen from a suitable distance, appear as a continuum. These are known as object points. It is usual in computer graphics fields to quantize the object to be displayed into a series of planar facets that approximate to the actual shape. The points that make up the object are populated onto these facets. An observer viewing such an object from a sufficiently large distance will tend to see not the individual points but instead the complete object as if it were drawn with continuous lines or areas of colour. For this to occur there must be a sufficient density of points such that the eye cannot distinguish between adjacent points. The human eye can resolve two points if the angle subtended from the eye to the points is typically greater than one minute of arc (290.mu. radians). By knowing the minimum eye to object distance likely to arise, a minimum object point population density can be calculated.
The facets themselves will generally be of differing sizes and will abut each other at different angles. If the object has curves, then the smaller these facets are, the closer they are able to provide a true representation of these curved areas. The facets will then be populated with object points. Each of these points forms a basic element of the picture, and taken together, these points make up the object to be displayed.
If it is desired to show part of an image having a continuous surface, there should be no sudden changes in object point population density. On a single facet, there is no problem in obtaining such a uniform density. However, when facets are joined together at different angles, the points will, in general, not flow from one facet to the other and still keep a localised uniform density. This leads to problems of non uniform density of object points across facet boundaries: too high a density will produce a bright area, whereas too low a density will produce a dark area on the object.